Liquid fuse



Jan. 8, 1935. R H. EARLE 1,987,055

LIQUID FUSE Filed May 2l, 1952 2 Sheets-Sheet l @.wwimm lll(- www moeufor v faf/ @M MM a ttorneg R. H. EARLE LIQUID FUSE `lan. 8, 1935. I

Filed May 21, 1932 2 Sheets-Shedl 2 TJMEQX Jnventor orneg Patented Jan. 8, 1935 UNITED STATES PATENT OFFICE Application May Z1, 1932, Serial No. 612,762

9 Claims.

This invention relates to liquid fuses and is particularly directed to a link for a liquid fuse and the associated parts therefor.

Objects of this invention are to provide a liquid fuse in which the link is so formed that one portion thereof responds to moderate prolonged overloads, and another portion thereof is so formed that it responds to substantially quickly applied higher overloads.

Further objects are to provide a liquid fuse in which the fuse link is formed of two portions which preferably overlap and are joined by a low melting point solder, and in which an are extinguishing liquid is provided, the fuse link being drawn down into the liquid upon rupturing of the fuse, and the construction being such that means are provided adjacent the soldered portion of the fuse so that although the solder melts at a higher point than the boiling'point of the liquid, that nevertheless the fuse will respond to moderate overloads as gas is trapped around the soldered portion of the fuse and is held at such point, thereby holding the liquid out of contact withk such portion of the fuse link and allowing the fuse link to accurately respond to a predetermined overload, although the fuse link is employed in a liquid fuse structure.

Further and more specific objects are to provide a novel form of fuse link for a liquid fuse in which the fuse link is formed withan intermediate portion composed of two overlapping parts joined together by a low melting point solder, and which is also provided with a spaced portion of reduced cross-section, the soldered overlapping portion responding to moderate overloads, and the reduced portion having a greater current carrying capacity than the soldered portion, but nevertheless, due to the peculiar construction of the fuse, responds substantially in- -io stantly to higher overloads before the soldered portions have time to separate, whereby a unitary fuse link is provided, two portions of which respond to different values or types of overloads.

Embodiments of the inventions are shown in the accompanying drawings, in which:

Figure l is a side elevation of a liquid fuse embodying one form of this invention, parts of the structure being broken away and shown in section.

Figure 2 is a view, in section, corresponding to the upper portion of Figure 1.

Figure 3 is an enlarged transverse sectional view on the line 3-3 of Figure 2.

Figure 4 is a fragmentary enlarged detail showing' a; further form of fuse link,

Figure 5 is a view showing a further form of the invention.

Figure 6 is a chart showing the relation between the time and the current values at which the fusie will respond.

Referring to the drawings, it will be seen that the fuse comprises a tubular liquid carrying body portion 1 provided with an upper contact 2 and a lower contact 3. A fuse link is electrically connected to the upper and lower contacts. It may be supported in any suitable manner, as by means of the arched support 4 forming the subject matter of my co-pending application for Liquid fuses, Serial No. 609,452 filed May 5, 1932.

The fuse link comprises a pair of strips 5 which extend downwardly and which receive between them the upwardly extending strip 6 oi the lower portion of the fuse link. The overlapped portions are reduced to provide the reduced section intermediate portion 7, see particularly Figure 2.

The lower portion of the fuse link is secured to a fitting 8 in any suitable manner, such fitting being in turn connected to the flexible leader 9 extending to the lower contact 3 and to the tension spring 10 so that the fuse is maintained under tension.

It is preferable to provide an additional short length of fuse strip, as indicated at 1l, for the lower portion of the fuse and to bring this small section of the fuse link up to the reduced portion 7, as shown most clearly in Figures 1 and 2. These two portions may be secured together by a rivet l2, or in any other suitable manner.

The upper portion of the fuse link is provided with an aperture 13 which extends through both of the strips 5 and provides a reduced section adapted to respond substantially instantly to higher overloads than that for which the intermediate section 7 is designed to respond.

The intermediate section 7 formed of the overlapping reduced sections, has these reduced sections joined by a low melting point solder.

However, inasmuch as this solder melts at a point higher than the boiling point of the liquid, means are provided which act to trap gases formed by the boiling of the liquid when the intermediate section is heated, and to hold these gases in contact with the intermediate section '7, displacing the liquid therefrom and preventing chilling of the intermediate section by this liquid.

This is especially desirable so that the intermediate section can respond at the precise value of overload for which the device has been calibrated. If, on the other hand, the liquid had been allowed to remain in contact with the interso construct the fuse link that the low melting mediate section and a small prolonged overload occurred, the liquid might chill the intermediate section sufliciently to prevent fusing of the solder at this precise overload, thereby upsetting the accurate calibration of the fuse. However, with this invention such a. defect is avoided.

One mode of carrying out this idea is to provide a slotted cork 14 which substantially encloses the intermediate section 7, the slot being indicated at 15 in Figures 2 and 3. It is clear that the cork itself provides minute air spaces and in addition, due to the constriction of the portion surrounding the fuse, the free passage of liquid therethrough during the evolution of gas is prevented and gas is more or less trapped in contact with the reduced section and chilling of such reduced section by the liquid is thereby prevented.

Another way of carrying out this inventive idea is shown in Figure 5. In this form of the invene tion a cylinder 16 is provided and surrounds the intermediate section 7. This cylinder may be formed in any manner so as to provide somewhat of a heat insulating structure, so that the gases evolved within the cylinder are'not condensed on the side walls of the cylinder due to the cooling of the liquid on the outer side of the side walls. For example as shown in Figure 5, the cylinder may be made of bakelite, fiber, or of any other material, or in any other manner, to secure this result. It is provided with a relatively tightly fitting upper portion 17 through which the fuse link passes, and which lits the fuse link with sufficient accuracy to prevent the too free entrance of liquid within the cylinder when the fuse link is heated and gases are formed within the cylinder.

It is also provided with a bottom portion 18 which has an aperture 19 slightly larger than the fuse link so as to allow the liquid to be displaced by the gases generated within the cylinder due to the heating of the intermediate portion 'l of the fuse link. In this way gases are trapped around the intermediate section and the chilling of the liquid is prevented.

In the form of fuse link shown in Figure 4 a reduced section is provided both in the upper and lower portion ofthe fuse link by means of the apertures 20 and 21, such upper and lower portions' being indicated by the reference characters 22 and 23 respectively. The intermediate portion is indicated by the reference character 24 and corresponds to the intermediate portion 7 hereinbefore described.

It is preferable in all forms of the invention to point solder allows the intermediate portion to separate at a lower load than either the upper or lower portions. The upper or the lower portion, or both, is adapted to respond to higher overloads in a substantially instantaneous manner, and due to the means for preventing chilling of the intermediate portion by the liquid, such intermediate portion is adapted to respond to a prolonged and lesser overload. For example, if the intermediate soldered section is designed to respond to a twenty-five ampere current, as indicated by the curve 25 of Figure 6, it has been found from actual tests that it will fuse after a certain critical time interval in the construc- 'tion illustrated.

For example considering the curve indicated at 25 in Figure 6, it will be seen that the intermediate section melts its solder and separates at the point marked X on the time axis, whh corresponds to the point marked Y on the axis of amperes. There is, therefore, a certain time interval required for the fusing of this portion of the fuse link with a twenty-five ampere load. For a greater overload, for instance for a suddenly applied overload in excess of twenty-five amperes, a certain time interval is required even for a dead short circuit, as indicated by the upwardly curving portion of the curve 25 in Figure 6. To shorten this interval, the cross-section of the exposed or unshielded portions of the fuse link has been reduced, as by means of the opening 13 in Figure 2 or the openings 20 and 21 in Figure 4, the cross-sectional area at such points corresponding to a thirty ampere solid fuse, for instance..

This portion of the fuse link, for a quickly applied overload, fuses very much quicker than that required to melt the solder for the overlapped portions, as'indicated by the curve 26 in Figure 6,

which is the curve plotted between amperes and time yfor the upper and lower portions of the fuse link and corresponds to a thirty ampere solid fuse link. It is clear, therefore, that the advantage of the substantially instantaneous fusing of the solid link is combined with the more slowly responding soldered portion for a smaller overload, so that the fuse link forming the subject matter of this invention has both the advantages of the soldered link and of the solid link.

Actual tests have shown that the Vresponse to overload with reference to time and value of overload follows the curve 25 up to the point X, Y

and thereafter follows the curve 26 from this point on as the overload is increased. Thus a very quickly responsive fuse link is provided which not only has this characteristic but also has the characteristic of responding to a, relatively small overload, which overload is maintained for a greater interval of time. g

As shown in my copending application hereinabove referred to, it is to be noted that a soft gasket disk is clamped by the upper ring nut against the upper contact. The disk is formed of a yielding and somewhat expansible material such as lead, aluminum, tinfoil, or some other alloy which is soft and expansible. The disk, when clamped in place by the ring nut, forms a gas seal, and is adapted to be ruptured.

Also as shown in the drawings and as described in greater detail in my copending application, a protecting means, in the form of a cap provided with spring fingers as shown in Figure 5 of the drawings, may be employed to mechanically protect the soft yielding gasket.

The liquidl level in the fuse may be anywhere desired, provided it covers the cork and the major portion ofthe fuse link. It is usually filled approximately to the liquid level indicated by the reference character L in Figures 1, 2 and 5. It is clear, therefore, that any excessive pressure due to boiling ofthe liquid is relieved by bulging of the diaphragm if this pressure reaches such a point. Also it is obvious that when the fuse blows, the diaphragm and the protecting disk are blown away from the fuse tube.

It will be seen, therefore, that a novel form vof fuse link and liquid fuse construction has been provided by this invention, in which a unitary link responds substantially instantly to quickly applied overloads above a certain point, and yet responds also to a smaller overload maintained for a greater length of time, and that means have been provided to prevent the chilling of the intermediate or soldered section of the link by the arc extinguishing liquid of the liquid fuse.

Although this invention has been described in considerable detail, it is to be understood that such description is intended as illustrative rather than limiting, as the invention may be variously embodied and is to be interpreted as claimed.

I claim:

1. A liquid fuse comprising an upper and a lower contact, a liquid carrying tubular body portion, a fuse link electrically joined to said contacts, a spring placing said fuse link in tension, said fuse link having an intermediate part formed of two overlapping sections soldered together, and a protecting member at the soldered overlapping portion of said link for substantially holding the liquid out of contact with said soldered overlapping portion when such portion becomes heated, said protecting member having a restricted opening to permit the escape of gas and to retard the entrance of liquid.

2. A liquid fuse comprising an upper and a lower contact, a liquid carrying tubular body portion, a fuse link electrically joined to said contacts, a spring placing said fuse link in tension, said fuse link having an intermediate part formed of two overlapping sections soldered together, and a protecting member covering substantially the entire soldered overlapping portion of said link for substantially holding the liquid out of contact with said soldered overlapping portion when such portion becomes heated, said protecting member having a restricted opening to permit the escape of gas and to retard the entrance of liquid.

3. A liquid fuse comprising a liquid carrying tubular body portion provided with spaced contacts, a fuse link electrically connected to said contacts, a spring placing said fuse link under tension, said link having a portion adapted to separate under prolonged overloads of a predetermined value, and means substantially surrounding said portion for trapping gas adjacent said portion when said portion becomes heated, said means having a restricted opening to permit the escape of gas and to retard the entrance of liquid, whereby the liquid is temporarily held out of contact with such portion.

4. A liquid fuse comprisinga liquid carrying tubular body portion having spaced contacts, a fuse link electrically connected to said contacts, a spring placing said fuse link in tension, said fuse link having an intermediate portion formed of overlapping parts held together by a low melting point solder, and means substantially surrounding said soldered portion and having a portion open only at the bottom acting to hold gas generated by the heating of the fuse link in contact with the fuse link adjacent the soldered section, whereby contact of the liquid with such section is prevented when the fuse link is heated to la point sufficient to vaporize the liquid.

5. A liquid fuse comprising a liquid carrying tubular body portion provided with upper and lower contacts, a fuse link electrically connected to said contacts, means for placing said link under tension, said link having an intermediate part formed of overlapping portions joined by a low melting point solder, and a heat insulator substantially surrounding said portion and acting to trap gas and hold the liquid out of contact with said portion of the fuse link when said fuse link is heated sufficiently to vaporize the liquid adjacent said portion, said insulator having a restricted opening to permit discharge of gas and restricting the entrance of liquid.

6. In a liquid fuse, a liquid carrying body portion provided with spaced contacts, a fuse link electrically connected to said contacts and having an intermediate portion adapted to separate under overloads of a predetermined value, and a member substantially surrounding said portion and having a hollow interior for trapping gas and holding the liquid out of contact with said portion of the fuse link when said fuse link is heated during overloads, said member permitting the free and unrestricted separation of the intermediate portion of said fuse link without requiring the destruction of said member, said member having a gas discharge opening adjacent its lower end only.

7. A liquid fuse comprising a liquid carrying tubular body portion having spaced contacts, a fuse link electrically connected to said contacts and having an intermediate portion formed of overlapping parts joined by a low melting point solder, a gas trapping cylinder surrounding said intermediate portion and having a top wall and having a bottom wall provided with means permitting the egress of liquid when gas is formed within said cylinder due to the heating of said intermediate portion during overload, said cylinder being closed at all points except its bottom wall.

8. A liquid fuse comprising a liquid carrying tubular body portion having spaced contacts, a fuse link electrically connected to said contacts, said fuse link having a portion designed to respend to prolonged overloads and another portion designed to respond to substantially quickly applied overloads of greater magnitude, and means substantially surrounding said ist mentioned portion of said fuse link for holding the liquid out of contact with said rst mentioned portion when subjected to prolonged overloads, said means being closed at all points except its bottom, whereby a gas pocket is formed when the first mentioned portion of said fuse link is heated, whereby said fuse accurately responds to prolonged overloads of a predetermined value and substantially instantly responds to overloads of a greater value.

9. A liquid fuse comprising an upper and lower contact, a liquid carrying, tubular body portion, a fuse link electrically joined to said contacts, a spring placing said fuse link in tension, said fuse link having at least two distinctly different sections, one section of said fuse link having relatively long, reduced width overlapping portions joined by a solder having a melting point above the boiling point of said liquid and adapted to respond to prolonged relatively small overloads, the other section of said fuse link having a reduced portion of a larger current carrying capacity than said rst mentioned section and adapted to quickly respond to large overloads at a speed greater than the speed of response of said rst mentioned section, and a gas trapping member surrounding the said first mentioned soldered section and being attached adjacent its upper portion only to said fuse link and being provided with a gas discharge opening in its lower portion only, whereby upon small overloads gas is trapped in said gas trapping member and a heat insulating zone is thereby produced for said soldered section.

RALPH H. EARLE. 

